At the present time, electronic products are used in almost every aspect of life, and the heart of these electronic products is the integrated circuit. Integrated circuits are used in many portable electronic products, such as cell phone, portable computers, voice recorders, etc. as well as in many larger electronic systems, such as cars, planes, industrial control systems, etc.
Integrated circuits are made in and on silicon wafers by extremely complex systems that require the coordination of hundreds or even thousands of precisely controlled processes to produce a finished semiconductor wafer. Each finished semiconductor wafer has hundreds to tens of thousands of integrated circuits, each worth hundreds or thousands of dollars.
Integrated circuits are made up of hundreds to millions of individual components. One common component is the semiconductor integrated circuit transistor. The integrated circuit transistors contain polysilicon gates on silicon oxide gates, or gate oxides, over the silicon substrate. On the sides of the polysilicon gates, the silicon substrate is doped to become conductive. A curved silicon oxide or silicon nitride spacer, referred to as a “sidewall spacer”, is formed on the sides of the polysilicon gate.
To complete the integrated circuit, a silicon oxide dielectric layer is deposited to cover the polysilicon gate, the curved spacer, and the silicon substrate. To provide electrical connections for the integrated circuit, openings are etched in the silicon oxide dielectric layer to the polysilicon gate and the source/drain junctions. The openings are filled with metal to form electrical contacts. To complete the integrated circuits, the contacts are connected to additional levels of wiring in additional levels of dielectric material to the outside of the dielectric material.
In operation, an input signal to the gate contact to the polysilicon gate controls the flow of electric current from one source/drain contact through one source/drain junction through the channel to the other source/drain junction and to the other source/drain contact.
As integrated circuits have decreased in size, it has been found that the electrical resistance between the metal contacts and the silicon substrate or the polysilicon has increased to the level where it negatively impacts the performance of the integrated circuits. To lower the electrical resistance, a transition material is formed between the metal contacts and the silicon substrate or the polysilicon. The best transition materials have been found to be cobalt silicide (CoSi2) and titanium silicide (TiSi2).
The silicide is formed by first applying a thin layer of the cobalt or titanium on the silicon substrate over the source/drain junctions and the polysilicon gates. The process is generally referred to as “siliciding”. Since the shallow trench oxide and the sidewall spacers will not react to form a silicide, the silicides are aligned over the source/drain junctions and the polysilicon gates so the process is also referred to as “self-aligned siliciding”, or “saliciding”.
However, as integrated circuits have decreased even further in size, it has been discovered that problematic short-circuits are occurring in the transistors which appear to be related to the silicide.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.